This invention relates to a novel optical information recording member, to methods for preparing such a member, and to methods for recording and retrieving information from such a member.
It is known in the prior art to construct an optical recording member, to optically record information on such a member, and to optically recover information from such a member. In Landwer U.S. Pat. No. 3,825,323, there is disclosed a "laser writing" or recording process used to generate a memory by localized melting of selected areas along recording tracks in the surface of a thermo-plastic film. In such a process, the laser beam is selectively focused on the surface of a moving film to cause minute melted depressions in the surface of the film. In recording binary data on such an optical recording member, the melted depressions and areas with no melts correspond to the bits of information 1's and 0's. Such recorded information can be optically read out later by various known means. Due to the extremely small size of the focused laser beam which is used, a very large amount of information can be recorded on a given area of such an optical recording member. For example, Landwer reports that over four million individual bits of binary data have been recorded per square inch or record surface. It is clear that such a memory device for information has great utility.
In Spong, U.S. Pat. No. 4,097,895, there is disclosed a multilayer optical record which is made of a glass substrate, a thin reflective layer of metal, and a topcoat of an organic dye. An information track may be formed on the surface of such an optical record by exposing it to a laser beam which is controlled in accordance with the information to be recorded. The information track is composed of a series of spaced pits formed by the varporization of the organic dye in the areas exposed to high intensity beam. Similarly, in Bloom et al U.S. Pat. No. 4,023,185, other organic dyes useful in ablative optical recording medium are disclosed.
Since the laser or writing instrument must melt or ablate the active layer in such an optical recording member to form a melted depression or a pit in such active layer to record a bit of information, it is clear that the size of the laser apparatus required as well as the amount of energy consumed per bit depends on the nature of the materials which make up the active layer as well as the thickness of that layer. For example, the active layer should have a high absorbance at the wavelength of the laser beam. The active layer should also be as thin as possible to minimize the amount of energy required for ablation. Other factors to be considered in determining the materials to be used in the active layer include ease of handling and fabrication, stability before and after information has been recorded on the recording member, and that those materials be inexpensive, readily available, and economical to use in the fabricating process. Accordingly, there is a need for improved optical recording members of the type indicated above.